// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MEMORY_REF_COUNTED_H_
#define BASE_MEMORY_REF_COUNTED_H_

#include <stddef.h>

#include <cassert>
#include <iosfwd>
#include <type_traits>

#include "base/atomic_ref_count.h"
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/macros.h"
#ifndef NDEBUG
#include "base/logging.h"
#endif
#include "base/threading/thread_collision_warner.h"
#include "build/build_config.h"

namespace base {

namespace subtle {

    class BASE_EXPORT RefCountedBase {
    public:
        bool HasOneRef() const { return ref_count_ == 1; }

    protected:
        RefCountedBase()
            : ref_count_(0)
#ifndef NDEBUG
            , in_dtor_(false)
#endif
        {
        }

        ~RefCountedBase()
        {
#ifndef NDEBUG
            DCHECK(in_dtor_) << "RefCounted object deleted without calling Release()";
#endif
        }

        void AddRef() const
        {
            // TODO(maruel): Add back once it doesn't assert 500 times/sec.
            // Current thread books the critical section "AddRelease"
            // without release it.
            // DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#ifndef NDEBUG
            DCHECK(!in_dtor_);
#endif
            ++ref_count_;
        }

        // Returns true if the object should self-delete.
        bool Release() const
        {
            // TODO(maruel): Add back once it doesn't assert 500 times/sec.
            // Current thread books the critical section "AddRelease"
            // without release it.
            // DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#ifndef NDEBUG
            DCHECK(!in_dtor_);
#endif
            if (--ref_count_ == 0) {
#ifndef NDEBUG
                in_dtor_ = true;
#endif
                return true;
            }
            return false;
        }

    private:
        mutable int ref_count_;
#ifndef NDEBUG
        mutable bool in_dtor_;
#endif

        DFAKE_MUTEX(add_release_);

        DISALLOW_COPY_AND_ASSIGN(RefCountedBase);
    };

    class BASE_EXPORT RefCountedThreadSafeBase {
    public:
        bool HasOneRef() const;

    protected:
        RefCountedThreadSafeBase();
        ~RefCountedThreadSafeBase();

        void AddRef() const;

        // Returns true if the object should self-delete.
        bool Release() const;

    private:
        mutable AtomicRefCount ref_count_;
#ifndef NDEBUG
        mutable bool in_dtor_;
#endif

        DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
    };

} // namespace subtle

//
// A base class for reference counted classes.  Otherwise, known as a cheap
// knock-off of WebKit's RefCounted<T> class.  To use this, just extend your
// class from it like so:
//
//   class MyFoo : public base::RefCounted<MyFoo> {
//    ...
//    private:
//     friend class base::RefCounted<MyFoo>;
//     ~MyFoo();
//   };
//
// You should always make your destructor non-public, to avoid any code deleting
// the object accidently while there are references to it.
template <class T>
class RefCounted : public subtle::RefCountedBase {
public:
    RefCounted() { }

    void AddRef() const
    {
        subtle::RefCountedBase::AddRef();
    }

    void Release() const
    {
        if (subtle::RefCountedBase::Release()) {
            delete static_cast<const T*>(this);
        }
    }

protected:
    ~RefCounted() { }

private:
    DISALLOW_COPY_AND_ASSIGN(RefCounted<T>);
};

// Forward declaration.
template <class T, typename Traits>
class RefCountedThreadSafe;

// Default traits for RefCountedThreadSafe<T>.  Deletes the object when its ref
// count reaches 0.  Overload to delete it on a different thread etc.
template <typename T>
struct DefaultRefCountedThreadSafeTraits {
    static void Destruct(const T* x)
    {
        // Delete through RefCountedThreadSafe to make child classes only need to be
        // friend with RefCountedThreadSafe instead of this struct, which is an
        // implementation detail.
        RefCountedThreadSafe<T,
            DefaultRefCountedThreadSafeTraits>::DeleteInternal(x);
    }
};

//
// A thread-safe variant of RefCounted<T>
//
//   class MyFoo : public base::RefCountedThreadSafe<MyFoo> {
//    ...
//   };
//
// If you're using the default trait, then you should add compile time
// asserts that no one else is deleting your object.  i.e.
//    private:
//     friend class base::RefCountedThreadSafe<MyFoo>;
//     ~MyFoo();
template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T>>
class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
public:
    RefCountedThreadSafe() { }

    void AddRef() const
    {
        subtle::RefCountedThreadSafeBase::AddRef();
    }

    void Release() const
    {
        if (subtle::RefCountedThreadSafeBase::Release()) {
            Traits::Destruct(static_cast<const T*>(this));
        }
    }

protected:
    ~RefCountedThreadSafe() { }

private:
    friend struct DefaultRefCountedThreadSafeTraits<T>;
    static void DeleteInternal(const T* x) { delete x; }

    DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
};

//
// A thread-safe wrapper for some piece of data so we can place other
// things in scoped_refptrs<>.
//
template <typename T>
class RefCountedData
    : public base::RefCountedThreadSafe<base::RefCountedData<T>> {
public:
    RefCountedData()
        : data()
    {
    }
    RefCountedData(const T& in_value)
        : data(in_value)
    {
    }

    T data;

private:
    friend class base::RefCountedThreadSafe<base::RefCountedData<T>>;
    ~RefCountedData() { }
};

} // namespace base

//
// A smart pointer class for reference counted objects.  Use this class instead
// of calling AddRef and Release manually on a reference counted object to
// avoid common memory leaks caused by forgetting to Release an object
// reference.  Sample usage:
//
//   class MyFoo : public RefCounted<MyFoo> {
//    ...
//   };
//
//   void some_function() {
//     scoped_refptr<MyFoo> foo = new MyFoo();
//     foo->Method(param);
//     // |foo| is released when this function returns
//   }
//
//   void some_other_function() {
//     scoped_refptr<MyFoo> foo = new MyFoo();
//     ...
//     foo = NULL;  // explicitly releases |foo|
//     ...
//     if (foo)
//       foo->Method(param);
//   }
//
// The above examples show how scoped_refptr<T> acts like a pointer to T.
// Given two scoped_refptr<T> classes, it is also possible to exchange
// references between the two objects, like so:
//
//   {
//     scoped_refptr<MyFoo> a = new MyFoo();
//     scoped_refptr<MyFoo> b;
//
//     b.swap(a);
//     // now, |b| references the MyFoo object, and |a| references NULL.
//   }
//
// To make both |a| and |b| in the above example reference the same MyFoo
// object, simply use the assignment operator:
//
//   {
//     scoped_refptr<MyFoo> a = new MyFoo();
//     scoped_refptr<MyFoo> b;
//
//     b = a;
//     // now, |a| and |b| each own a reference to the same MyFoo object.
//   }
//
template <class T>
class scoped_refptr {
public:
    typedef T element_type;

    scoped_refptr()
        : ptr_(NULL)
    {
    }

    scoped_refptr(T* p)
        : ptr_(p)
    {
        if (ptr_)
            AddRef(ptr_);
    }

    // Copy constructor.
    scoped_refptr(const scoped_refptr<T>& r)
        : ptr_(r.ptr_)
    {
        if (ptr_)
            AddRef(ptr_);
    }

    // Copy conversion constructor.
    template <typename U,
        typename = typename std::enable_if<
            std::is_convertible<U*, T*>::value>::type>
    scoped_refptr(const scoped_refptr<U>& r)
        : ptr_(r.get())
    {
        if (ptr_)
            AddRef(ptr_);
    }

    // Move constructor. This is required in addition to the conversion
    // constructor below in order for clang to warn about pessimizing moves.
    scoped_refptr(scoped_refptr&& r)
        : ptr_(r.get())
    {
        r.ptr_ = nullptr;
    }

    // Move conversion constructor.
    template <typename U,
        typename = typename std::enable_if<
            std::is_convertible<U*, T*>::value>::type>
    scoped_refptr(scoped_refptr<U>&& r)
        : ptr_(r.get())
    {
        r.ptr_ = nullptr;
    }

    ~scoped_refptr()
    {
        if (ptr_)
            Release(ptr_);
    }

    T* get() const { return ptr_; }

    T& operator*() const
    {
        assert(ptr_ != NULL);
        return *ptr_;
    }

    T* operator->() const
    {
        assert(ptr_ != NULL);
        return ptr_;
    }

    scoped_refptr<T>& operator=(T* p)
    {
        // AddRef first so that self assignment should work
        if (p)
            AddRef(p);
        T* old_ptr = ptr_;
        ptr_ = p;
        if (old_ptr)
            Release(old_ptr);
        return *this;
    }

    scoped_refptr<T>& operator=(const scoped_refptr<T>& r)
    {
        return *this = r.ptr_;
    }

    template <typename U>
    scoped_refptr<T>& operator=(const scoped_refptr<U>& r)
    {
        return *this = r.get();
    }

    scoped_refptr<T>& operator=(scoped_refptr<T>&& r)
    {
        scoped_refptr<T>(std::move(r)).swap(*this);
        return *this;
    }

    template <typename U>
    scoped_refptr<T>& operator=(scoped_refptr<U>&& r)
    {
        scoped_refptr<T>(std::move(r)).swap(*this);
        return *this;
    }

    void swap(T** pp)
    {
        T* p = ptr_;
        ptr_ = *pp;
        *pp = p;
    }

    void swap(scoped_refptr<T>& r)
    {
        swap(&r.ptr_);
    }

    explicit operator bool() const { return ptr_ != nullptr; }

    template <typename U>
    bool operator==(const scoped_refptr<U>& rhs) const
    {
        return ptr_ == rhs.get();
    }

    template <typename U>
    bool operator!=(const scoped_refptr<U>& rhs) const
    {
        return !operator==(rhs);
    }

    template <typename U>
    bool operator<(const scoped_refptr<U>& rhs) const
    {
        return ptr_ < rhs.get();
    }

protected:
    T* ptr_;

private:
    // Friend required for move constructors that set r.ptr_ to null.
    template <typename U>
    friend class scoped_refptr;

    // Non-inline helpers to allow:
    //     class Opaque;
    //     extern template class scoped_refptr<Opaque>;
    // Otherwise the compiler will complain that Opaque is an incomplete type.
    static void AddRef(T* ptr);
    static void Release(T* ptr);
};

template <typename T>
void scoped_refptr<T>::AddRef(T* ptr)
{
    ptr->AddRef();
}

template <typename T>
void scoped_refptr<T>::Release(T* ptr)
{
    ptr->Release();
}

// Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
// having to retype all the template arguments
template <typename T>
scoped_refptr<T> make_scoped_refptr(T* t)
{
    return scoped_refptr<T>(t);
}

template <typename T, typename U>
bool operator==(const scoped_refptr<T>& lhs, const U* rhs)
{
    return lhs.get() == rhs;
}

template <typename T, typename U>
bool operator==(const T* lhs, const scoped_refptr<U>& rhs)
{
    return lhs == rhs.get();
}

template <typename T>
bool operator==(const scoped_refptr<T>& lhs, std::nullptr_t null)
{
    return !static_cast<bool>(lhs);
}

template <typename T>
bool operator==(std::nullptr_t null, const scoped_refptr<T>& rhs)
{
    return !static_cast<bool>(rhs);
}

template <typename T, typename U>
bool operator!=(const scoped_refptr<T>& lhs, const U* rhs)
{
    return !operator==(lhs, rhs);
}

template <typename T, typename U>
bool operator!=(const T* lhs, const scoped_refptr<U>& rhs)
{
    return !operator==(lhs, rhs);
}

template <typename T>
bool operator!=(const scoped_refptr<T>& lhs, std::nullptr_t null)
{
    return !operator==(lhs, null);
}

template <typename T>
bool operator!=(std::nullptr_t null, const scoped_refptr<T>& rhs)
{
    return !operator==(null, rhs);
}

template <typename T>
std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p)
{
    return out << p.get();
}

#endif // BASE_MEMORY_REF_COUNTED_H_
